It seems that Project Harmony has finally taken itself public. From the website:
Project Harmony is a community-centered group focused on contributor agreements for free and open source software (FOSS).
In reality, this seems to be a closed group that in no way represents the community in general and mainly acts in the interest of various corporations. Their goal is to create a bunch of templates for contracts to make participating in free software projects even more complicated than it already is.
Look, we have a bunch of copyright licenses. They're not always easy to understand, and there's enough details and corner cases and interactions with the real world to make your head hurt. My head as well. (They're still easier, and more standardized, than contracts for proprietary software.)
Contributing to a free software project is easy enough, in most cases. You make a patch, and if the project accepts it, yay. Your patch will be licensed the same way as all the other code.
These Harmony agreements aim at making you give up your copyright to someone else, usually a corporate sponsor of the project. That's a bad thing.
If the corporation owns the copyright, or you give them a license to do anything they wish with the project, they can do all sorts of evil things with it. For example, they can release it under a non-free license, or enter into complicated patent agreement with someone else that will require you to pay protection money later on, or something else. There is no end to the evil corporations invent, when given the chance.
If, however, you refuse to give the corporation any ownership, or special powers, then their ability to do evil lessens, or at least you aren't helping them do that.
It might be possible to use the Harmony agreements, as they are currently written, in ways that do not directly allow evil. However, why bother? By sticking to well-known, court-tested free software free software licenses, there is no need for the Harmony licenses. You get to keep the corporations honest, without having to read piles more legalese.
Another way of looking at this: here's a bunch of corporations that want you to start using complicated legal documents for their benefit. Ask yourself, in what scenario is this going to be a good idea for you?
Just say no to copyright assignments.